Design of urban electric bus systems

Abstract

Many public transport authorities have a great interest in introducing zero-emission electric buses. However, the transformation process from diesel to electric bus systems opens up a vast design space which seems prohibitive for a systematic decision making process. We present a holistic design methodology to identify the 'most suitable system solution' under given strategic and operational requirements. The relevant vehicle technologies and charging systems are analysed and structured using a morphological matrix. A modular simulation model is introduced which takes technical and operational aspects into account. The model can be used to determine a feasible electric bus system. The technology selection is based on a detailed economic analysis which is conducted by means of a total cost of ownership (TCO) model. To cope with uncertainties in forecasting, a stochastic modelling of critical input parameters is applied and three different future scenarios are evaluated. The applicability of the model was verified in a pilot project in Berlin and the methodology was applied to a realistic operational scenario. Our results indicate that electric bus systems are technically feasible and can become economically competitive from the year 2025 under the conditions examined.

Conceptual Design of Urban E-Bus Systems with Special Focus on Battery Technology

“…In this section, we will give an overview to battery and charging systems and discuss the technical parameters most important for electric bus system design. For a discussion of other relevant components like body, drivetrain and auxiliaries and their influence on electric bus system design we refer to Göhlich et al (2018). .…”

“…Despite recent advances in material and manufacturing processes of Li-ion batteries, the battery persists to be the limiting factor in terms of drive range and lifespan of the vehicle. A recent work, Göhlich et al (2018), identified three most competitive Li-ion battery chemistries and corresponding charging strategies, lithium iron phosphate (LFP), lithium titanium oxide (LTO) and lithium nickel manganese cobalt oxide (NMC) for E-bus systems and performed a total cost of ownership (TCO) analysis. While the work provides a holistic and thorough cost analysis, rather simplistic battery aging models have been used and therefore, their lifespans have been conservatively estimated.…”

“…For an in-depth comparison of the technologies for e-bus applications, the parameters in Table 3 are obtained from the following assumptions. We assume a setup from Göhlich et al (2018), a 12-meter bus capable of supporting a maximum passenger density of 4 people/m², which leaves approximately 3400 kg for the battery system. However, not all could be allocated to the cells and the presence of electronics and cooling equipment reduces the effective energy density of the whole battery systems roughly by a factor of 0.6.…”

“…However, OC 1 and OC 2 do not require such a large battery as it becomes an unnecessary payload to carry. For OC 1 and OC 2, we determine the size of the batteries such that the SoC window swings between 30-70% in case of worst case usage scenarios depicted in Göhlich et al (2018). This is to limit high-cycle fatigue of the battery.…”

Implementation Schemes for Electric Bus Fleets at Depots with Optimized Energy Procurements in Virtual Power Plant Operations

“…The rollout of mobility solutions is accompanied by substantial challenges in the transport and energy sector. This includes, for example, the reduction of the total cost of ownership, the provision of sufficient charging infrastructures, the agreement of standards, and the formulation of regulatory requirements [1,2]. For charging processes and the provision of active energy management, a variety of limiting factors has to be taken into account [3], e.g., distance traveled, road topology, driving behavior, prevailing traffic conditions, and ambient temperature.…”